Generally, all domestic corporations must file form 1120 by the 15th day of the 4th month after the end of its tax year. This includes,
However, a corporation with a fiscal tax year ending June 30 must file by the 15th day of the 3rd month after the end of its tax year.
A corporation with a short tax year ending anytime in June will be treated as if the short year ended on June 30, and must file by the 15th day of the 3rd month after the end of its tax year.
If the due date falls on a Saturday, Sunday, or legal holiday, the corporation can file on the next business day.
In case, you need additional time to file your income tax return after the regular due date, file Form 7004 to the IRS. This gives you an automatic 6-month time to file your income tax return. Generally, the corporation must file Form 7004 by the regular due date of the return to extend the due date.